Retinal dopamine (DA) and melatonin may play a role in regulating light sensitivity in the eye. Depletion of DA increases light sensitivity, making animals photophobiology Augmentation of DA turnover inhibits the retinal degeneration induced by constant intensity light illumination, while melatonin administration increases it (Bubenik Purtill, 1980). Melatonin may cause aggregation of eye pigments and increased transmission of light to retina. These two neuroactive compounds are produced in the eye with diurnal rhythms which are opposite to one another - retinal DA turnover is greatest in the light phase of the cycle when melatonin production is lowest and retinal melatonin production is highest at night when DA turnover is reduced. Consequently, at night the result of a low DA and high melatonin production might be expected to be increased sensitivity to light (and , conversely, decreased sensitivity during the day). Dopamine and melatonin are produced from the dietary amino acids, tyrosine (TYR) and tryptophan (TRP), respectively. The level of TYR AND TRP in tissue influences the rate at which these substances are produced (Wurtman, 1982). Increase or decreases in brain levels of these amino acid precursors (produced by their direct injection or by consumption of protein or carbohydrate-containing meals) results in parallel changes in nomoamine synthesis and release. Brain TYR and TRP level is determined not only by their plasma concentration but also by the concentration of the neutral amino acids (leucine, isoleucine, valine, phenylalanine) which compete with them for brain uptake. Thus, factors which affect plasma levels of the neutral amino acids will influence brain TYR and TRP concentration (e.g. diabetes and alcohol consumption reduce brain TYR and TRP level). It is not known whether the same type of carrier mechanism for amino acid uptake exists at the retinal-blood barrier. Preliminary studies indicate that TYR administration increase retinal TYR level and, in light-activated retina, increases DA turnover. The proposed pilot study will investigate whether changes in plasma amino acid pattern (produced by meal or ethanol consumption, or diabetes) will influence retinal TYR and TRP uptake and, if so, whether fluctuations in the retinal precursor will influence the synthesis of DA and melatonin.